A variety of environmental and life changes alter human circadian rhythms, and in some individuals cause physiological and psychological problems. Variation in entrained circadian rhythms, due to sex and chronotype, and problems of rhythm disruptions are likely the result of differences in sensitivity or responsiveness to entertaining photic and non-photic environmental cues, such as the light/dark cycle and social interactions. Entrainment of the circadian system by the light/dark cycle has been studied at many levels of analysis particularly in nocturnal rodents. In contrast, a number of non-photic stimuli have been identified that alter entrained or free-running circadian rhythms, but we have only a limited idea of how these stimuli reach the circadian system because most non-photic stimuli are complex and employ multiple sensory systems. A better understanding of how non-photic stimuli interact with the circadian system will best be developed with a zeitgeber that engages only one sensory system. Octodon degus serve as an ideal model for exploration of the interaction of non-photic entrainers of the circadian system and determination of the neural underpinnings of those interactions. Degus are a highly social, diurnal rodents, displaying rhythms similar to those of humans , which are entrained by light and social interactions. Hypotheses to be tested by this proposal focus on how social interactions of degus are able to entrain circadian rhythms. Aim 1. Determine whether olfactory cues delivered to the main olfactory system are sufficient to entrain circadian system. Experiments will examine whether airborne odor cues can replace social interactions for accelerated re-entrainment following phase shifts and entrain animals in constant conditions by phase advances and delays. Aim 2: Delineate the critical components of the neural circuitry transmitting odor cues to the circadian system. Experiments will use tract tracing, selective lesions and Fos immunohistochemistry to determine the functional neuroanatomy involved in the entertainment of circadian rhythms by olfactory/social stimuli. Successful completion of the proposed research will produce the first detailed behavioral/neuroanatomical model of the interaction of non-photic zeitgeber and the circadian clock. This work with degus will eventually allow the investigators to analyze the interactions between photic and non-photic entraining cues in the control of circadian rhythms in a diurnal, social mammal with many properties similar to humans, and may lead to non-photic treatments for circadian disruptions.